Collagen, the protein that is present in the largest amount in a human body, plays an extremely important role as connective tissue that is a component of the extracellular matrix. Examples of tissue that contain large quantities of collagen include skin, bone tissue, tendon, ligament, and the like. As these tissues age, wrinkles or sagging, osteoporosis and the like are caused, and the major cause of these is thought to be a decrease in amount, degeneration or the like of tissue collagen.
It is known that collagen synthesis is stimulated by the action of vitamins, hormones, cytokines and the like, and it is also known that amino acids that are the building blocks of proteins also promote collagen synthesis. It has been reported from studies using fibroblasts that glutamine promoted collagen synthesis (G. Bellon et al., Biochimica Biophysica Acta, 1995, 1268, 311-323), and also from studies of wound healing using humans or animals that arginine alone or a mixture of arginine, β-hydroxy-β-methylbutyric acid, and glutamine promoted collagen synthesis at wound sites (US005733884A, US20030091601A1, and J. Z. Williams et al., Annals of surgery, 2002, 369-375).
Further, although collagen protein or a collagen-composing amino acid composition and the like are commercially available as products that promote collagen synthesis, the effects of these are not clear, and a demand exists for amino acids or an amino acid composition that possesses an excellent effect.